Three patterns of extra-testicular venous drainage in the rabbit. Divergence from a traditional concept.

Seventy-eight male New Zealand white rabbits were autopsied and found to have variable left extra-testicular venous anatomy. Our observations reveal that in the rabbit the left testis is drained in one of three ways, identified as either A (18%), B (30%) or C (52%)--type drainage. The right testicular vein in all cases drained directly into the inferior vena cava immediately superior to the right iliolumbar vein. In type A drainage, the left testicular vein drained directly into the inferior vena cava at the level of the left iliolumbar vein. In type B drainage, the left testicular vein emptied into the left iliolumbar vein, which in turn drained into the inferior vena cava. In type C drainage both the left testicular and iliolumbar veins anastomosed to form a "lumbotesticular" trunk which emptied directly into the left renal vein. These three patterns of left venous vascular anatomy in the rabbit can be explained on the basis of their embryologic development. Our observations suggest that it is the caudal segment of the left pelvic subcardinal vein and its anastomosis with the caudal cardinal complex which persist as the left testicular vein and that the more cranial segment of this vein, heretofore presumed to remain patent, atrophies to the level of the developing left renal vein.